Determining power headroom in a wireless network

ABSTRACT

Methods and apparatus for power control are described. Methods are included for calculating and signaling power control related data to support multiple component carriers (CCs) for which transmission may be accomplished with one or more WTRU power amplifiers (PAs). Methods are included for calculating and signaling one or more of CC-specific power control related data and PA-specific power control related data. The power control related data may include one or more of maximum power, power headroom, and transmit power. Methods for selecting which power control related data to exchange are included. Methods are included for calculating and signaling power control related data for physical UL shared channel (PUSCH), physical UL control channel (PUCCH), and simultaneous PUSCH and PUCCH transmission.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Nos.61/247,676 filed on Oct. 1, 2009; 61/248,373 filed on Oct. 2, 2009;61/285,343 filed on Dec. 10, 2009; 61/329,194 filed on Apr. 29, 2010;and 61/356,472 filed on Jun. 18, 2010, the contents of which are herebyincorporated by reference herein.

FIELD OF THE INVENTION

This application is related to wireless communications.

BACKGROUND

Transmit power of a wireless transmit/receive unit (WTRU) may bedetermined in the WTRU based on measurements made by the WTRU and datareceived from an evolved NodeB (eNodeB). The WTRU transmit power controlmay be used for maintaining quality of service (QoS), controllingintercell interference, maximizing a WTRU's battery life and the like.

In Third Generation Partnership Project (3GPP) long term evolution(LTE), uplink (UL) power control may be used to compensate for long-termfading, (including path loss and shadowing), while reducing inter-cellinterference, and avoiding occurrences of the WTRU having to invoke itsmaximum power procedure to prevent its power amplifier (PA) fromoperating beyond its linear region and/or to prevent the WTRU fromexceeding maximum transmit power limits imposed by the network,regulatory requirements, and the like. LTE power control methods mayinclude combined open loop and closed loop power control methods. In LTERelease 8 (R8) and 9 (R9), the WTRU transmits on a single carrier overone antenna which may be accomplished with one power amplifier (PA).Open and closed loop power control related data are exchanged betweenthe eNodeB and the WTRU for the single transmit path.

In LTE R8 and R9, power headroom may be used for assisting the eNodeB toschedule the UL transmission resources of different WTRUs. In LTE, powerheadroom, reported from the WTRU to the eNodeB, is the differencebetween the nominal WTRU maximum transmit power and the estimated powerfor PUSCH transmission for the single carrier. Maximum transmit powerimposed by the network for the single carrier is signaled by the eNodeBto the WTRU in system information. Additional limits such as the WTRU'spower class, its PA capabilities, and the like, may reduce the maximumtransmit power used by the WTRU for the headroom calculation.

LTE R8 and R9 methods for calculating and signaling power headroom andother power control related data may not be sufficient to supportmultiple component carriers (CCs) which may require multiple WTRU PAs.

SUMMARY

Methods and apparatus for power control are described. Methods areincluded for calculating and signaling power control related data tosupport multiple component carriers (CCs) for which transmission may beaccomplished with one or more WTRU power amplifiers (PAs).

Methods are included for calculating and signaling one or more ofCC-specific power control related data and PA-specific power controlrelated data. The power control related data may include one or more ofmaximum power, power headroom, and transmit power. Methods for selectingwhich power control related data to exchange are included. Methods areincluded for calculating and signaling power control related data forphysical UL shared channel (PUSCH), physical UL control channel (PUCCH),and simultaneous PUSCH and PUCCH transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIGS. 2-4 are example flowcharts of a method of signaling of CC-specificheadroom; and

FIG. 5 is an example diagram illustrating a power headroom reportingmethod.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116, though it will be appreciated that thedisclosed embodiments contemplate any number of WTRUs, base stations,networks, and/or network elements. The RAN 104 may also be incommunication with the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managementgateway (MME) 142, a serving gateway 144, and a packet data network(PDN) gateway 146. While each of the foregoing elements are depicted aspart of the core network 106, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 142 may be connected to each of the eNode-Bs 142 a, 142 b, 142 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

In LTE Release 8 (R8), a WTRU reports (i.e., signals or transmits) powerheadroom (PH) for one carrier to the base station. When conditionswarrant the WTRU sending a PH report (PHR), the WTRU waits until atransmission interval (TTI) for which the WTRU receives a valid uplink(UL) physical uplink shared channel (PUSCH) grant, i.e., UL resources,and then sends the PHR in that TTI.

In LTE-A, a WTRU may report power headroom for one, two or morecomponent carriers (CCs) to the eNodeB. When conditions warrant the WTRUmay send a PHR for at least one UL CC, PHRs for all active UL CCs, orPHRs for all configured UL CCs, for example if there is no explicitactivation mechanism, and even if there is no UL grant for the specificTTI for a given UL CC. For the UL CCs which do not have a PUSCH grant,the WTRU may use a reference format or grant (i.e., a set of grantparameters known to both the WTRU and the base station) to derive the PHfor that UL CC.

Consequently, the WTRU may report PH for some combination of UL CCs withactual PUSCH grants and reference PUSCH grants. UL CCs with actualgrants in a given TTI are referred to herein as real CCs or transmittedCCs. UL CCs that do not have actual grants, and may use referencegrants, for the PH calculation are referred to herein as fake or virtualCCs.

The base station may use the PHRs from WTRUs in deciding how to scheduleUL resources in the future for these WTRUs. Due to the possibility oftransmission on multiple CCs which may be implemented in the WTRU withone or more PAs, the base station may not have enough information tomake appropriate scheduling decisions using the existing PH calculationsand reports.

In another aspect of LTE-A, a WTRU supporting UL transmission overmultiple antenna ports may operate in multi-antenna port mode in whichit may transmit over multiple antenna ports or single antenna port modein which it may transmit over one antenna port. While in multi-antennaport mode, the base station may dynamically signal the WTRU to switchbetween the configured transmission scheme of the transmission mode anda single-antenna port scheme in which the WTRU may only transmit overone antenna port. Switching to the single-antenna port scheme isreferred to herein as fallback. For each PUSCH transmission, thesignaled UL grant from the base station may direct the WTRU to useeither the transmission scheme of the configured transmission mode orthe single-antenna port fallback scheme. Power headroom may be differentupon such change. In accordance with existing R8 reporting rules, theWTRU may not report such a change until the next periodic power headroomreport, which may be too far in the future to enable the base station tomake appropriate scheduling choices for the current transmission scheme.

Described herein are power control methods and apparatus for LTE Release10 (R10) or LTE-A that may address bandwidth extension using carrieraggregation, multiple CCs, multiple power amplifiers, uplinkmultiple-input multiple-output (UL MIMO), simultaneous PUSCH andphysical uplink control channel (PUCCH) transmission, and fallback. Themethods include associating CCs with PAs, and configuring and reportingpower control parameters related to the CCs and PAs; power headroomreporting for PUSCH, PUCCH, and simultaneous PUSCH and PUCCHtransmissions; and computing and reporting power headroom to enable thebase station to make informed scheduling decisions. Each of the examplemethods presented may be used individually or in combination with anyone or more of the other example methods.

In the examples described below, the mapping of CCs to PAs may be knownby both the WTRU and the base station. If the mapping of CCs to PAs fora WTRU is determined in the base station, the base station may signalthe mapping of (J) CCs to (K) PAs to the WTRU. Alternatively, if themapping of CCs to PAs for a WTRU is determined in the WTRU, the WTRU maysignal the mapping of (J) CCs to (K) PAs to the base station.Alternatively, the mapping may be derived by both the WTRU and the basestation based on known, defined or pre-established configurations (e.g.,by WTRU category and frequency band). The number of the PAs at the WTRUmay be derived by the base station implicitly from the WTRU categoryinformation (or other indicator) signaled by the WTRU (e.g., as part ofthe WTRU capability information). Alternatively, the WTRU may explicitlysignal the number of the PAs and their characteristics, (e.g., maximumtransmit power) to the base station.

In certain of the examples described below, the WTRU may signal powercontrol data to the eNodeB for one or more (J) CCs using one or more (K)PAs. To illustrate such a mapping, consider the following mappingexample between WTRU CCs and PAs as shown in Table 1 below. Three CCsare transmitted using two PAs, (i.e., K=2 and J=3), band CC#1 istransmitted by PA#1 and CC#2 and CC#3 are transmitted by PA#2.

TABLE 1 CC PA 1 1 2 2 3In the examples described herein, P_(CC)(i,j) represents the required ULtransmit power determined by the WTRU for CCj in subframe i before anyreduction for a maximum power limitation.

Described herein is an example method for signaling CC-specific maximumpower. In the example method, the base station may signal P_(Max), theparameter used to limit the WTRU's uplink transmission power on acarrier frequency, on a per CC basis to the WTRU. For J CCs, thisrequires J such values, denoted P_(Max)(j) or P-Max(j).

In further examples described herein P_(Max)(j) and P-Max(j) may be usedinterchangeably to represent the CC specific maximum transmit powervalue signaled to the WTRU for each CCj. P_(CMAX)(j) is used torepresent the CC specific maximum transmit power value for CCj, whichmay take into account one or more of the signaled maximum power value,P_(Max)(j), the maximum power of the WTRU power class, maximum powerreduction allowances, tolerances, and the like. P_(CMAX)(j) may bereferred to as the configured maximum power, configured maximum transmitpower, or configured maximum output power for the CC.

Described herein are example methods for signaling and/or determiningPA-specific maximum power. In an example method, each PA k may have amaximum transmit power capability, denoted P_(AMAX) (k), that may bedetermined by the WTRU. P_(AMAX)(k) may be an attribute of the WTRUcategory. Separate maximum power transmit capability for each PA may besignaled by the WTRU to the base station. For KPAs, this requires Kmaximum transmit power capabilities. Alternatively, both the WTRU andthe base station may derive the PA specific maximum transmit powercapability based on the WTRU category (or other indicator) reported tothe base station by the WTRU in a WTRU capability information element.Additionally, the base station may signal a substitute PA-specificmaximum transmit power capability to the WTRU. The substitutePA-specific maximum transmit power capability may be a value differentfrom the PA property value that may be signaled from the WTRU to thebase station as stated above. This may require the WTRU to operate asthough the PA had the substitute maximum transmit power capability. Thesubstitute maximum transmit power capability may be less than themaximum transmit power capability which is the property of the PA.

Described herein are example methods for signaling and/or determiningCC-specific power headroom and/or PA-specific power headroom. In anexample method, separate power headroom reports for each CC and PA maybe signaled to the base station by the WTRU. For J CCs and K PAs, thismay require J+K headroom reports. The CC power headroom may be thedifference between the CC maximum transmit power and the requiredtransmit power for all physical uplink shared channel (PUSCH)transmissions on the CC. The PA power headroom may be the differencebetween the PA maximum transmit power and the required transmit powerfor all PUSCH transmissions at the PA.

Alternatively, the WTRU may signal the power headroom reports for the JCCs and the base station may derive the K PA headroom values based onthe CCs to PAs mapping, the CC headroom reports, P-Max(j) for each CC_j,and the PA-specific maximum transmit power.

Described herein is an example method for signaling CC-specific transmitpower and PA-specific transmit power. In the example method, separatetransmit powers for each CC and PA may be signaled to the base stationby the WTRU. For J CCs and KP As, this may require J+K transmit powerreports. The headroom for CC j in subframe i, denoted P_(HCC)(i,j), maybe determined by the base station from the CC transmit powers as:P _(HCC)(i,j)=P-Max(j)−P _(CC)(i,j),  Equation (1)where P_(CC)(i,j) is the required transmit power for PUSCH transmissionin CC(j) in subframe i.

The headroom for PA k in subframe i, denoted P_(HPA) (i,k), may bedetermined by the base station from the PA transmit powers as:P _(HPA)(i,k)=P _(AMAX)(k)−P _(PA)(i,k)  Equation (2)where P_(PA)(i,k) is the required transmit power for all PUSCHtransmissions in PA(k) in subframe i.

Described herein is a method for reporting headroom or transmit power.In the example method, the base station may configure the WTRU as towhether transmit power and/or power headroom is reported by the WTRU.The transmit power and/or power headroom may be CC specific and/or PAspecific.

Described herein is a method for signaling CC-specific transmit power.In the example method, the WTRU may signal CC-specific transmit power tothe base station and the base station may determine, from theCC-specific transmit powers, the PA-specific headroom. The WTRU may notneed to explicitly signal the PA transmit power or headroom. This mayrequire J rather than J+K transmit power reports, and may reduce thesignaling overhead. The PA headroom for PA k in subframe i, denotedP_(HPA) (i,k), may be determined from the CC transmit powers and the CCto PA mapping. Using the CC to PA mapping example provided earlier:P _(HPA)(i,1)=P _(AMAX)(1)−P _(CC)(i,1), and  Equation (3)P _(HPA)(i,2)=P _(AMAX)(2)−(P _(CC)(i,1)+P _(CC)(i,2)).  Equation (4)and the headroom for the CCs, denoted P_(HCC)(i,j), may be determined bythe base station using Equation 1, copied below for convenience:P _(HCC)(i,j)=P-Max(j)−P _(CC)(i,j),  Equation (1)

Described herein are example methods for transmit power and/or powerheadroom reporting for simultaneous PUSCH/PUCCH transmissions. In LTE,PUCCH and PUSCH are transmitted in different subframes in order toprimarily preserve the single carrier property in UL transmission. Inaddition, the LTE WTRU reports power headroom based on the PUSCHtransmit power. LTE-A, however, may support, simultaneous PUSCH andPUCCH transmissons, where a single WTRU-specific UL CC is configuredsemi-statically for carrying PUCCH. When simultaneous PUSCH/PUCCHtransmission occurs in a subframe (on a CC), the maximum transmit poweravailable for the PUSCH transmission may be reduced by the transmitpower allocated to the PUCCH transmission. In this case, it may bedesirable to include the PUCCH transmit power value in the transmitpower and/or power headroom reporting, since the PUCCH transmissiondirectly affects the power headroom available for PUSCH. In the examplemethods described herein, the WTRU may take PUCCH transmit power intoaccount when reporting to the base station the WTRU's power headroom ortransmit power in which simultaneous PUSCH and PUCCH transmission occurson a CC.

In one example method, if simultaneous PUSCH and PUCCH transmissionoccurs on CC j, the transmit power and/or headroom of PUSCH and PUCCHmay be combined. For transmit power reporting the WTRU may report:P _(CC)(i,j)=P _(CC) _(_) _(PUSCH)(i,j)+P _(CC) _(_)_(PUCCH)(i,j),  Equation (5)where P_(CC) _(_) _(PUCCH)(i,j) may be the required transmit power forPUSCH on CC j in subframe i (i.e., the PUSCH power before any reductionfor a maximum power limitation) and P_(CC) _(_) _(PUCCH)(i,j) may be therequired transmit power for PUCCH on CC j in subframe i (i.e., the PUCCHpower before any reduction for a maximum power limitation). If insubframe i (where PUSCH power headroom may be reported), PUCCH is notpresent, then the latest required transmit power for PUCCH (i.e., latestPUCCH transmission) on CC j may used for P_(CC) _(_) _(PUCCH)(i,j).Alternatively, the downlink control information (DCI) format used forthe latest PUCCH transmission may be used to derive P_(CC) _(_)_(PUCCH)(i,j). Alternatively, a reference DCI format (e.g., DCI format1a) may be used to derive P_(CC) _(_) _(PUCCH)(i,j).

For power headroom (PH) reporting, the WTRU may report:

$\begin{matrix}{{{P_{HCC}( {i,j} )} = {{P_{CMAX}(j)} - {10*\log\; 10\{ {10^{\frac{P_{CC\_ PUSCH}{({i,j})}}{10}} + 10^{\frac{P_{CC\_ PUCCH}{({i,j})}}{10}}} \}}}},} & {{Equation}\mspace{14mu}(6)}\end{matrix}$where P_(CMAX)(j) may be the configured maximum power for CC j, (e.g.,carrier specific maximum transmit power) as described earlier. If insubframe i (where PUSCH power headroom may be reported), if PUCCH is notpresent, then the latest required transmit power for PUCCH on CC j mayused for P_(CC) _(_) _(PUCCH)(i,j). Alternatively, the DCI format usedfor the latest PUCCH transmission may be used to derive P_(CC) _(_)_(PUCCH)(i,j). Alternatively, a reference DCI format (e.g., DCI format1a) may be used to derive P_(CC) _(_) _(PUCCH)(i,j).

On the other CC(s) (l≠j), the WTRU may report the transmit power and/orpower headroom of PUSCH. For transmit power reporting, the WTRU mayreport P_(CC)(i,l)=P_(CC) _(_) _(PUSCH)(i,l) and for power headroomreporting, the WTRU may report P_(HCC)(i,l)=P_(CMAX)(l)−P_(CC) _(_)_(PUSCH)(i,l).

In another example method, the WTRU may separately/individually reporttransmit power and/or power headroom reports for PUSCH and PUCCH. Fortransmit power reporting, the WTRU may report: P_(CC) _(_) _(PUSCH)(i,j)and P_(CC) _(_) _(PUCCH)(i,j). For power headroom reporting, the WTRUmay report:P _(HCC) _(_) _(PUSCH)(i,j)=P_(CMAX)(j)−P_(CC) _(_) _(PUSCH)(i,j);and  Equation (7)P _(HCC) _(_) _(PUCCH)(i,j)=P_(CMAX)(j)−P _(CC) _(_)_(PUCCH)(i,j),  Equation (8)where P_(HCC) _(_) _(PUSCH)(i,j) and P_(HCC) _(_) _(PUCCH)(i,j) mayrepresent the power headroom reports for PUSCH and PUCCH, respectively,and PUCCH is transmitted on CC j. If in subframe i, (where PUSCH powerheadroom may be reported), if PUCCH is not present, then the latestrequired transmit power for PUCCH on CC j may be used for P_(CC) _(_)_(PUCCH)(i,j). Alternatively, the DCI format used for the latest PUCCHtransmission may be used to derive P_(CC) _(_) _(PUCCH)(i,j).Alternatively, a reference DCI format (e.g., DCI format 1a) may be usedto derive P_(CC) _(_) _(PUCCH)(i,j). For the other CC(s) (l≈j), the WTRUmay report the transmit power and/or power headroom of PUSCH on the CC.

In another example method, the WTRU may separately report transmit powerand/or power headroom for PUSCH as in LTE and for the combination ofPUSCH and PUCCH if PUCCH is present on the CC (e.g., CC j). For transmitpower reporting, the WTRU may report (for subframe i) P_(CC) _(_)_(PUSCH)(i,j) and P_(CC)(i,j), where P_(CC)(i,j)=_(CC) _(_)_(PUSCH)(i,j)+P_(CC) _(_) _(PUCCH)(i,j). For power headroom reportingthe WTRU may report P_(HCC) _(_) _(PUSCH)(i,j), where P_(HCC) _(_)_(PUSCH)(i,j)=P_(CMAX)(j)−P_(CC) _(_) _(PUSCH)(i,j) and P_(HCC)(i,j) isas shown in Equation 6 and copied here for convenience:

$\begin{matrix}{{{P_{HCC}( {i,j} )} = {{P_{CMAX}(j)} - {10*\log\; 10\{ {10^{\frac{P_{CC\_ PUSCH}{({i,j})}}{10}} + 10^{\frac{P_{CC\_ PUCCH}{({i,j})}}{10}}} \}}}},} & {{Equation}\mspace{14mu}(6)}\end{matrix}$where P_(CMAX)(j) may be the configured maximum power for CC j, (e.g.,carrier specific maximum transmit power) as described earlier.

Described are example methods for transmit power and/or power headroomreporting when there are multiple PUCCHs per CC. For the case of morethan one PUCCH within a CC, P_(CC) _(_) _(PUCCH)(i,j) may be replacedwith

${\sum\limits_{n}{P_{CC\_ PUCCH}( {i,j,n} )}},$where there are N instances of PUCCH in CC j in subframe i, denoted asP_(CC) _(_) _(PUCCH)(i,j,n) for n=0, 1, . . . N−1. Alternatively, theremay be separate headroom or transmit power reports for each such PUCCH.

Described are example methods for triggering reports. For simultaneousPUSCH and PUCCH transmission, the power headroom reporting mechanism maybe based on timer and/or event triggers. However, the value of the timerand/or event threshold may be different for PUSCH, PUCCH and/or thecombination of PUSCH and PUCCH. For a power headroom or transmit powerreport based on one timer and/or event threshold, the WTRU may reportthe power headroom or transmit power of the channel which is associatedwith the given timer or event threshold. Alternatively, the WTRU mayreport the power headroom or transmit power of both PUSCH and PUCCH onceeither channel's timer expires or the event threshold is exceeded.Alternatively, the WTRU may report power headroom or transmit power ofboth PUSCH and PUCCH upon triggers from both channels. Alternatively,the WTRU may report PUCCH power headroom along with PUSCH power headroomwhenever PUSCH power headroom reporting is triggered.

With regard to which of the above triggers and reporting methods may beused by a WTRU, it may be specified, configured by the base station forall WTRUs in the cell via a system information block (SIB), orconfigured by the base station individually for each WTRU in the cellvia a radio resource control (RRC) message.

Described herein are example methods for configurable transmit power orpower headroom reporting in carrier aggregation situations. The numberof PAs with which a WTRU may be equipped may be different depending onWTRU class (or category). In addition, the CC allocation/configurationfor a WTRU may be dependent on several factors such as WTRU class, QoSrequirement, CC availability, and other like factors. The transmit poweror power headroom on a CC may be close to that on other CC(s), forexample, in contiguous CC allocation. Therefore in one example method,the base station may configure the WTRU to report transmit power orpower headroom per CC, or per group of CCs (like contiguous CCs), or forall active/configured CCs, e.g., based on the carrier aggregationallocation and/or the WTRU PA configuration, and/or some other systemparameters.

Alternatively, the WTRU may autonomously determine which transmitpower(s) or power headroom(s) is/are reported, e.g., based on apredefined rule. For example, if |P_(HCC)(i,k)−P_(HCC)(i,n)|≦ε where eis a predefined threshold and k≠n, then send only a single powerheadroom value for both the k^(th) and n^(th) CC.

The above condition implies that if the difference in power headroombetween any CCs is small enough (or less than or equal to a predefinedvalue), then the WTRU may not report transmit power(s) or powerheadroom(s) on all the associated CCs, rather the WTRU may send a singlereport which represents all of the CCs. For example, this may be donefor the case of contiguous CCs. In this case, the WTRU may report atransmit power or power headroom corresponding to a representative CC(e.g., a middle CC or a CC with lowest (or highest) carrier frequency)among the contiguous CCs.

Described herein is an example method for signaling CC-specific powerheadroom. The example method may compute a CC-specific power headroom,denoted as P′_(HCC) (i,j), and signal the computed CC-specific headroomto a base station. The example method may not compute CC-specific powerheadroom in the conventional sense, i.e., as the difference betweenrequested (nominal based on last UL grant) and maximum CC-specifictransmit power. The notation P′_(HCC) (i,j) may be used to distinguishCC-specific power headroom computed per the example method below fromCC-specific power headroom computed in the conventional sense which usesthe notation P_(HCC)(i,j). This example method is referred to later asAlternative 1.

The base station may, by using the signaled CC-specific power headroomcomputed per the example method, schedule grants that avoid exceedingmaximum power in the CCs and avoid exceeding maximum power in the PAs.This may be accomplished without the base station having any knowledgeof the number of PAs, PA-specific maximum transmit power, PA-specificheadroom, CC-to-PA mapping, or the method used for the calculation.

The CC-specific headroom P′_(HCC) (i,j) may be signaled for all J CCsand may require J power headroom reports. Noting that the base stationis “unaware” and unaffected that the WTRU is using this method, theCC-specific power headroom P′_(HCC) (i,j) may be signaled as if thevalue is P_(HCC)(i,j). The trigger for signaling P′_(HCC) (i,j) may besimilar to that described for P_(HCC)(i,j), i.e., event based orperiodic, where the event is based on the value of P′_(HCC) (i,j) ratherthan P_(HCC)(i,j).

Referring to FIG. 2, the WTRU initiates computation of P′_(HCC) (i,j)(210). The power headroom for CC j in subframe i, denoted asP_(HCC)(i,j) [dB], may be determined for all J CCs as described inEquation 1 for PUSCH transmission or for simultaneous PUSCH and PUCCHtransmission as described in Equation 6, or some other unspecifiedcriteria for CC-specific power headroom (220). Define P^(w) _(HCC)(i,j)as P_(HCC)(i,j) in linear rather than dB form, as:

$\begin{matrix}{{P_{HCC}^{w}( {i,j} )} = {10^{\frac{{PMax}{(j)}}{10}} - 10^{\frac{P_{CC}{({i,j})}}{10}}}} & {{Equation}\mspace{14mu}(9)}\end{matrix}$

The power headroom for PA k in subframe i, denoted as P_(HPA)(i,k) [dB],may be determined for all K PAs as described in Equation 2 for PUSCHtransmission or for simultaneous PUSCH and PUCCH transmission asdescribed in Equation 6 or some other unspecified criteria forPA-specific power headroom (230). Define P^(w) _(HPA)(i,k) asP_(HPA)(i,k) in linear rather than dB form, as:

$\begin{matrix}{{P_{HPA}^{w}( {i,k} )} = {10^{\frac{P_{AMAX}{(k)}}{10}} - {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}{10^{\frac{P_{CC}{({i,j})}}{10}}.}}}} & {{Equation}\mspace{14mu}(10)}\end{matrix}$

The WTRU may then identify those CC(s) with positive linear headroom,i.e., P^(w) _(HCC)(i,j)≧0 and those CC(s) with negative linear headroom,i.e., P^(w) _(HCC)(i,j)<0 (240).

For each PA k, the WTRU may then determine the available PA power (250),denoted as P^(w) _(APA)(i,k), as the sum of P^(w) _(HPA)(i,k) plus thesum of P^(w) _(HCC)(i,j) for all CCs j mapped to PA k, and havingnegative P^(w) _(HCC)(i,j), or:

$\begin{matrix}{{{P_{APA}^{w}( {i,k} )} = {{P_{HPA}^{w}( {i,k} )} - {\sum\limits_{\mspace{14mu}\begin{matrix}{j❘{{{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}\mspace{11mu}\&}\mspace{14mu}{CC}}} \\{j\mspace{14mu}{has}\mspace{14mu}{negative}\mspace{14mu}{linear}\mspace{14mu}{headroom}}\end{matrix}}{P_{HCC}^{w}( {i,j} )}}}},} & {{Equation}\mspace{14mu}(11)}\end{matrix}$or, equivalently:

$\begin{matrix}{{{P_{APA}^{w}( {i,k} )} = {{P_{HPA}^{w}( {i,k} )} - {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}{\min( {0,{P_{HCC}^{w}( {i,j} )}} )}}}},} & {{Equation}\mspace{14mu}(12)} \\{\mspace{20mu}{where}} & \; \\{\mspace{20mu}{{P_{APA}^{w}( {i,k} )} \geq {{P_{HPA}^{w}( {i,k} )}.}}} & {{Equation}\mspace{14mu}(13)}\end{matrix}$

For each PA k, the WTRU may identify the PA as being one of three cases,denoted as A, B and C below (260). For each such case, the signaledCC-specific power headroom is computed as described.

The case in which the available PA power is positive and greater than orequal to the sum of positive CC-specific headroom reports is denoted ascase A. For any CCs that per grant computed power may exceed theirmaximum allowed power, the specific CCs' actual headroom may be signaledso that the base station may be expected to reduce, by future grant, theCC-specific transmit power to that maximum allowed power. The availablePA power may then be the original amplifier headroom plus that powergained by reducing the power of the negative-headroom CCs. In this case,the available power is more than the summed headroom reports of thepositive-headroom CCs, so the actual headroom reports for those CCs arealso signaled. If the base station were to fully utilize those headroomreports in a future grant, all CCs may be at their maximum transmitpower, and the PA may be below its maximum transmit power.

Referring now also to FIG. 3, in case A, for the available PA power,P^(w) _(APA)(i,k), being positive and greater than or equal to the sumof CC-specific power headroom reports for CCs identified as havingpositive headroom (310), i.e.,

$\begin{matrix}{{{{{P_{APA}^{w}( {i,k} )} \geq \sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k\mspace{14mu}\text{\&}\mspace{14mu}{CC}\mspace{14mu} j\mspace{14mu}{has}\mspace{14mu}{positive}\mspace{14mu}{linear}\mspace{14mu}{headroom}}}}\quad}{P_{HCC}^{w}( {i,j} )}},} & {{Equation}\mspace{14mu}(14)}\end{matrix}$or, equivalently:

$\begin{matrix}{{P_{APA}^{w}( {i,k} )} \geq {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}{{\max( {0,{P_{HCC}^{w}( {i,j} )}} )}.}}} & {{Equation}\mspace{14mu}(15)}\end{matrix}$then for all such CCs, the WTRU may report P′_(HCC) (i,j) as equal toP_(HCC)(i,j), i.e., the signaled CC-specific headroom is as originallydetermined (320).

The case in which the available PA power is positive and less than thesum of positive CC-specific headroom reports is denoted as case B and isalso shown in FIG. 3. For any CCs that per grant may exceed theirmaximum allowed power, their actual headroom may be signaled so that thebase station may be expected to reduce, by future grant, the CC-specifictransmit power to that maximum allowed power. The available PA power maythen be the original amplifier headroom plus that power gained byreducing the power of the negative-headroom CCs. In this case, theavailable power is less than the summed headroom reports of thepositive-headroom CCs, so the signaled headroom reports for thepositive-headroom CCs are their actual headroom reports reduced by someamount such that all of the available PA power is apportioned amongstthose CCs. If the base station were to fully utilize those headroomreports in a future grant, the formerly negative-headroom CCs may be attheir maximum transmit power, the formerly positive-headroom CCs may beat some higher (though below their maximum allowed) transmit power, andthe PA may be at its maximum transmit power.

In case B, for the available PA power, P^(w) _(APA)(i,k), being positiveand less than the sum of CC-specific headroom reports for CCs identifiedin Step 3 as having positive headroom (330), i.e.,

$\begin{matrix}{{0 \leq {P_{APA}^{w}( {i,k} )} < {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k\mspace{14mu}\text{\&}\mspace{14mu}{has}\mspace{14mu}{positive}\mspace{14mu}{headroom}}}{P_{HCC}^{w}( {i,j} )}}},} & {{Equation}\mspace{14mu}(16)}\end{matrix}$or, equivalently:

$\begin{matrix}{0 \leq {P_{APA}^{w}( {i,k} )} < {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}{{\max( {0,{P_{HCC}^{w}( {i,j} )}} )}.}}} & {{Equation}\mspace{14mu}(17)}\end{matrix}$then the WTRU may determine a weighting factor, denoted as α(i,k), tofully apportion the available power amongst the CCs identified as havingpositive headroom (335). For illustrative purposes only, one exampleweighting may be the quotient of the available power and the sum of thepositive CC-specific power headroom reports, or

$\begin{matrix}{{\alpha( {i,k} )}{\frac{P_{APA}^{w}( {i,k} )}{\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}{\max( {0,{P_{HCC}^{w}( {i,j} )}} )}}.}} & {{Equation}\mspace{14mu}(18)}\end{matrix}$

Other weightings may be possible (340), e.g., based on relative transmitpowers per positive-power headroom CC, in which case there may be aseparate weight for each CC j, denoted as α(i,j,k), or

$\begin{matrix}{{\alpha( {i,j,k} )}{\frac{P_{CC}^{w}( {i,{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}} )}{\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k\mspace{14mu}\text{\&}\mspace{14mu}{has}\mspace{14mu}{positive}\mspace{14mu}{headroom}}}{P_{CC}^{w}( {i,j} )}}.}} & {{Equation}\mspace{14mu}(19)}\end{matrix}$

Notwithstanding the method used to calculate α(i,k), after completingthe case B method, the weighting may be computed such that the sum ofthe power headroom reports of those CC(s) identified as having positiveheadroom is then equal to the available power.

For CCs identified as having positive headroom (345), the WTRU mayreport P′_(HCC) (i,j) as equal to P^(w) _(HCC)(i,j)·α(i,k), oralternatively, e.g., P^(w) _(HCC)(i,j)·α(i,j,k), converted to dB form,or

$\begin{matrix}{{{P_{HCC}^{\prime}( {i,j} )} = {{10 \cdot \log}\; 10( {10^{\frac{P_{HCC}{({i,j})}}{10}} \cdot {\alpha( {i,k} )}} )}},} & {{Equation}\mspace{14mu}(20)}\end{matrix}$or alternatively,

$\begin{matrix}{{P_{HCC}^{\prime}( {i,j} )} = {{10 \cdot \log}\; 10{( {10^{\frac{P_{HCC}{({i,j})}}{10}} \cdot {\alpha( {i,j,k} )}} ).}}} & {{Equation}\mspace{14mu}(21)}\end{matrix}$where the reported headroom for the positive-headroom CCs is now lowerthan or equal to as originally determined (350).

For CCs identified as having negative headroom (345), the WTRU mayreport P′_(HCC) (i,j) as equal to P_(HCC)(i,j) i.e., the signaledCC-specific headroom as originally determined (355).

The case in which the available PA power is negative is denoted as caseC and shown in FIG. 4. In this case, unlike case A and B, signalingactual headroom for the negative-headroom CCs and the base stationreducing their transmit power by future grant yields negative PAavailable power, i.e., such a grant may “request” that the PA transmitat a power higher than its maximum allowed power. This may be so even ifthe headroom for the positive-headroom CCs were signaled such that thebase station may reduce their transmit power by future grant to zerowatts. Therefore, negative headroom reports may be signaled for all CCssuch that the base station may reduce the transmit power by future grantof all CCs, such that a PA may be “requested” to transmit only at itsmaximum power, rather than exceed it. This is accomplished by first,similar to cases A and B, considering that if a future grant may reducethe transmit powers of the negative-headroom CCs to their maximums, whatmay be the resulting negative available PA power, i.e., a powershortage, and, second, by in some manner apportioning that shortageamongst all CCs such that the PA may be at its maximum transmit power.The CC-specific headroom reports are computed and signaled such that thebase station may, by future grant, request CC-specific transmit powersto achieve this effect, i.e., if the base station were to by futuregrant reduce all CC-specific transmit powers by their signaled negativeheadroom reports, all CCs may be below their maximum transmit power andalso lower than that requested by the previous grant, and the PA may beat its maximum transmit power. Note that in this case, the signaledheadroom reports are computed relative to the transmit power from theprevious grant, rather than as relative to the CC-specific maximumtransmit power. In either case, the desired effect should be realized.

In case C, for the available PA power, P^(w) _(APA)(i,k), beingnegative, i.e., P^(w) _(APA)(i,k)<0, then for the CCs (405) identifiedas having negative headroom (410), set a first temporary CC-specifictransmit power, denoted as P^(w1) _(CC)(i,j), to the maximum per-CCtransmit power (415) and for CCs identified as having positive headroom(410), set the first temporary CC-specific transmit power to therequested CC-specific transmit power (420). Then convert to linear form(425), or,

$\begin{matrix}{{{P_{CC}^{0}( {i,j} )} = \begin{Bmatrix}{P\;{{Max}(j)}} & {{P_{HCC}^{w}( {i,j} )} < 0} \\{P_{CC}( {i,j} )} & {{P_{HCC}^{w}( {i,j} )} \geq 0}\end{Bmatrix}},} & {{Equation}\mspace{14mu}(22)} \\{{P_{CC}^{w\; 1}( {i,j} )} = {10^{\frac{P_{CC}^{0}{({i,j})}}{10}}.}} & {{Equation}\mspace{14mu}(23)}\end{matrix}$

The WTRU may then compute a CC-specific weighting factor (430), denotedas β(i,j), from individual weighting factors assigned to each CC, as:

$\begin{matrix}{{{\beta( {i,j} )} = \frac{w( {i,j} )}{\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}{w( {i,j} )}}},} & {{Equation}\mspace{14mu}(24)}\end{matrix}$where w(i,j) may be a priority expressed as a numerical value in whichthe higher the value the higher the priority of the CC. For example,priority may be based on priority of the data or service supported bythe CC, CC-specific transmit power, P^(w1) _(CC)(i,j), modified by thedetermination of P^(w1) _(CC)(i,j) if applicable, some combinationthereof or some other criteria.

Note that β(i,j)≦1. That is, the weighting may be determined such that

${\sum\limits_{j}{\beta( {i,j} )}} = 1$and that after determining P^(w2) _(CC)(i,j), the sum of the CC-specifictransmit powers is equal to the maximum PA transmit power.

For all CCs, the WTRU may then compute a reduced second temporaryCC-specific transmit power, denoted as P^(w2) _(CC)(i,j), where theavailable power may be apportioned per the factor β(i,j) (440), or:P ^(w2) _(CC)(i,j)=P ^(w1) _(CC)(i,j)+β(i,j)·P ^(w)_(APA)(i,k).  Equation (25)

For all CCs, the WTRU may then compute the signaled headroom as theratio of reduced second CC-specific transmit power to that of theoriginal requested CC-specific transmit power, in dB (450), or:

$\begin{matrix}{P_{HCC}^{\prime} = {{10 \cdot \log}\; 10{( \frac{P_{CC}^{w\; 2}( {i,j} )}{P_{CC}^{w}( {i,j} )} ).}}} & {{Equation}\mspace{14mu}(26)}\end{matrix}$

Note that within Case C, the variables first and second “temporaryCC-specific transmit power” are intermediate variables used by themethod, neither PA nor CC transmit powers are set to these values.

Described herein is another example method for signaling CC-specificpower headroom. In this example method, the WTRU signals a modifiedCC-specific headroom, denoted as P′_(HCC) (i,j) below, to the basestation for all J CCs. The base station need not know the mapping of CCsto PAs, and the power control algorithm in the base station may be awareof the power headroom in each CC but does not know if the limitation isdue to P-Max or P_(AMAX). This example method may be referred to asAlternative 2.

The power headroom, denoted as P_(HCC)(i,j) for CC j in subframe i, maybe determined by the WTRU for all J CCs as shown in Equations 7 and 6,respectively, for PUSCH transmission or for simultaneous PUSCH and PUCCHtransmission.

The WTRU then determines and signals a modified power headroom for eachCC in the subframe as:P′ _(HCC)(i,j)=min(P _(HCC)(i,j),P _(HPA)(i,k)),  Equation (27)where P_(HPA)(i,k) is as described above, and CC j is mapped to PA k.

Described herein is an example method for power headroom reporting forcarrier aggregation when there may be a WTRU maximum power limit. Thesum of per component carrier transmit powers may be subject to somemaximum transmit power such that raising or lowering the transmit powerof one component carrier may impact the ability to raise the transmitpower in another component carrier. To account for this maximum transmitpower, an example method is included for calculating and signaling ofCC-specific power headroom when there is a WTRU maximum power limit.

For the case of the maximum WTRU transmit power, denoted as P_(UEMAX).being less than the sum of the per-CC maximum transmit powers, PMax(j),the first example method (Alternative 1) for signaling CC-specific powerheadroom may result in the WTRU reporting per-CC power headrooms thatmay result in the base station scheduling grants that may correspond toWTRU transmit power which exceeds maximum WTRU transmit power. In thefirst example method, the power constraints are per-CC maximum transmitpower, PMax(j), and per-PA maximum transmit power, P_(AMAX)(k). The basestation may, by using the signaled CC-specific power headroom from theWTRU, schedule grants that avoid exceeding maximum power in the CCs andavoid exceeding maximum power in the PAs.

In the present example method, the base station may, by using thesignaled CC-specific headroom from the WTRU, schedule grants that avoidexceeding maximum power in the CCs and maximum allowed transmit power ofthe WTRU, and optionally maximum power in the PAs. The mapping of theWTRU to CCs and, optionally, CCs to PAs, may be illustrated by theexample shown in Table 2 in which three CCs are transmitted by one WTRU,and the CCs may be mapped to two PAs.

TABLE 2 WTRU CC PA 1 1 1 2 2 3

For a given subframe, the nominal transmit power of the WTRU, i.e.,before any reduction by a maximum power procedure, in linear form, is

$\sum\limits_{j}{10^{\frac{P_{CC}{({i,j})}}{10}}.}$

Given the conventionally computed per-CC headroom(s), P_(HCC)(i,j), andthat the base station may schedule a future grant(s) such that the fulltransmit power capability of the WTRU may be scheduled, the transmitpower of the hypothetical future subframe, i+r, denoted as P^(w)_(WTRU)(i+r) may be

$\begin{matrix}{{P_{WTRU}^{w}( {i + r} )} = {{\sum\limits_{j}10^{\frac{P_{CC}{({i,j})}}{10}}} + {\sum\limits_{j}{P_{HCC}^{w}( {i,j} )}}}} & {{Equation}\mspace{14mu}(28)}\end{matrix}$

If P^(w) _(WTRU)(i+r) were to exceed P_(WTRUMAX) (in linear form), someor all of the reported per-CC power headrooms, P_(HCC)(i,j), may have tobe further reduced to avoid not only exceeding maximum power in the CCs,but also the maximum allowed transmit power of the WTRU.

An example method for modifying the reported per-CC power headrooms fromthe conventionally calculated headroom, P_(HCC)(i,j) is now described.The modified P_(HCC)(i,j) may be denoted as P″_(HCC)(i,j). Initially,define P^(w) _(HCC)(i,j) as P_(HCC)(i,j) in linear rather than dB, as:

$\begin{matrix}{{P_{HCC}^{w}( {i,j} )} = {10^{\frac{P\;{{Max}{(j)}}}{10}} - {10^{\frac{P_{CC}{({i,j})}}{10}}.}}} & {{Equation}\mspace{14mu}(29)}\end{matrix}$

The WTRU may determine the power headroom for the WTRU in subframe i,denoted as P_(HWTRU)(i) [dB]. Define P^(w) _(HWTRU)(i) as P_(HWTRU)(i)in linear form rather than dB form, as

$\begin{matrix}{{P_{HWTRU}^{w}(i)} = {10^{\frac{P_{WTRUMAX}}{10}} - {\sum\limits_{j}10^{\frac{P_{CC}{({i,j})}}{10}}}}} & {{Equation}\mspace{14mu}(30)}\end{matrix}$

The WTRU may then identify those CC(s) with positive linear headroom,i.e., P^(w) _(HCC)(i,j)≧0, and those CC(s) with negative linearheadroom, i.e., P^(w) _(HCC)(i,j)<0. The available WTRU power, denotedP^(w) _(AWTRU)(i), may be determined as P^(w) _(HWTRU)(i) plus the sumof P^(w) _(HCC)(i,j) for all CCs j having negative P^(w) _(HCC)(i,j),or:

$\begin{matrix}{{{P_{AWTRU}^{w}(i)} = {{P_{HWTRU}^{w}(i)} - {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{has}\mspace{14mu}{negative}\mspace{14mu}{linear}\mspace{14mu}{headroom}}}{P_{HCC}^{w}( {i,j} )}}}},} & {{Equation}\mspace{14mu}(31)}\end{matrix}$or, equivalently:

$\begin{matrix}{{{P_{AWTRU}^{w}(i)} = {{P_{HWTRU}^{w}(i)} - {\sum\limits_{j}{\min( {0,{P_{HCC}^{w}( {i,j} )}} )}}}}{where}{{P_{AWTRU}^{w}(i)} \geq {{P_{HWTRU}^{w}(i)}.}}} & {{Equation}\mspace{14mu}(32)}\end{matrix}$

Using one of the appropriate cases, denoted as cases A, B and C, theWTRU may compute and signal the CC-specific headroom.

For case A, where the available WTRU power, P^(w) _(AWTRU)(i), ispositive and greater than or equal to the sum of CC-specific headroomsfor CCs identified as having positive headroom, i.e.,

${{P_{AWTRU}^{w}(i)} \geq {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{has}\mspace{14mu}{positive}\mspace{14mu}{linear}\mspace{14mu}{headroom}}}{P_{HCC}^{w}( {i,j} )}}},$or equivalently:

${P_{AWTRU}^{w}(i)} \geq {\sum\limits_{j}{{\max( {0,{P_{HCC}^{w}( {i,j} )}} )}.}}$then the WTRU, for all CCs, may report P″_(HCC)(i,j) as equal toP_(HCC)(i,j).

For case B, where the available WTRU power, P^(w) _(AWTRU)(i), may bepositive and less than the sum of CC-specific headrooms for CCsidentified as having positive headroom, i.e.,

$0 \leq {P_{AWTRU}^{w}(i)} < {\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{has}\mspace{14mu}{positive}\mspace{14mu}{headroom}}}{P_{HCC}^{w}( {i,j} )}}$or, equivalently:

$0 \leq {P_{AWTRU}^{w}(i)} < {\sum\limits_{j}{{\max( {0,{p_{HCC}^{w}( {i,j} )}} )}.}}$then the WTRU may determine a weighting factor, denoted as α(1), tofully apportion the available power amongst the CCs identified as havingpositive headroom. For example, one possible such weighting is thequotient of the available power and the sum of the positive CC-specificheadrooms, or

$\begin{matrix}{{\alpha(i)} = \frac{P_{AWTRU}^{w}(i)}{\sum\limits_{j}{\max( {0,{P_{HCC}^{w}( {i,j} )}} )}}} & {{Equation}\mspace{14mu}(33)}\end{matrix}$

Other weightings are possible, e.g., based on relative transmit powersper positive-headroom CC. In this case, there may be a separate weightfor each CC j, denoted as α(i,j), or

$\begin{matrix}{{\alpha( {i,j} )} = {\frac{P_{CC}^{w}( {i,j} )}{\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{has}\mspace{14mu}{positive}\mspace{14mu}{headroom}}}{P_{CC}^{w}( {i,j} )}}.}} & {{Equation}\mspace{14mu}(34)}\end{matrix}$

Notwithstanding the particular method used to compute the weightingfactor, the weighting may be computed such that the sum of headrooms ofthose CC identified as having positive headroom(s) are then equal to theavailable power after computing P″_(HCC)(i,j) as described below.

For the CCs identified as having positive headroom, the WTRU may reportP″_(HCC)(i,j) as equal to P_(HCC)(i,j)α(i), or alternatively, P^(w)_(HCC)(i,j)α(i,j), which may be converted to dB form:

$\begin{matrix}{{{P_{HCC}^{''}( {i,j} )} = {{10 \cdot \log}\; 10( {10^{\frac{P_{HCC}{({i,j})}}{10}} \cdot {\alpha(i)}} )}},} & {{Equation}\mspace{14mu}(35)}\end{matrix}$or alternatively,

$\begin{matrix}{{P_{HCC}^{''}( {i,j} )} = {{10 \cdot \log}\; 10{( {10^{\frac{P_{HCC}{({i,j})}}{10}} \cdot {\alpha( {i,j} )}} ).}}} & {{Equation}\mspace{14mu}(36)}\end{matrix}$

Note that the reported headroom for the positive-headroom CCs is nowlower than or equal to P_(HCC)(i,j).

For CCs identified as having negative headroom, the WTRU may reportP″_(HCC)(i,j) as equal to P_(HCC)(i,j).

For case 3, where the available WTRU power, P^(W) _(AWTRU)(i) isnegative, i.e., P^(W) _(AWTRU)(i)<0, then the WTRU may, for the CCsidentified as having negative headroom, set a first temporaryCC-specific transmit power, denoted as P^(w1) _(CC)(i,j), to the maximumper-CC transmit power and for CCs identified as having positiveheadroom, set the first temporary CC-specific transmit power to therequested CC-specific transmit power. Converting these to linear form:

$\begin{matrix}{{P_{CC}^{0}( {i,j} )} = \begin{Bmatrix}{{PMax}(j)} & {{P_{HCC}^{w}( {i,j} )} < 0} \\{P_{CC}( {i,j} )} & {{P_{HCC}^{w}( {i,j} )} \geq 0}\end{Bmatrix}} & {{Equation}\mspace{14mu}(37)} \\{{P_{CC}^{w\; 1}( {i,j} )} = 10^{\frac{P_{CC}^{0}{({i,j})}}{10}}} & {{Equation}\mspace{14mu}(38)}\end{matrix}$

The WTRU may then convert a CC-specific weighting factor, denoted asβ(i,j) from individual weighting factors assigned to each CC, as:

$\begin{matrix}{{\beta( {i,j} )} = \frac{w( {i,j} )}{\sum\limits_{j❘{{CC}\mspace{14mu} j\mspace{14mu}{mapped}\mspace{14mu}{to}\mspace{14mu}{PA}\mspace{14mu} k}}{w( {i,j} )}}} & {{Equation}\mspace{14mu}(39)}\end{matrix}$where w(i,j) may be a priority expressed as a numerical value in whichthe higher the value the higher the priority of the CC. For example,this may be based on a priority of the data or service supported by theCC, a CC-specific transmit power (P^(w1) _(CC)(i,j)) modified bynegative or positive headroom if applicable, some combination thereof,or some other criteria.

Noting that β(i,j)≦1, and notwithstanding the method that may be usedfor CC-specific transmit power, the weighting may be determined suchthat the term

${\sum\limits_{j}{\beta( {i,j} )}} = 1$and that after computing P″_(HCC), the sum of the CC-specific transmitpowers may be equal to the maximum WTRU transmit power.

The WTRU may then, for all CCs, compute a reduced second temporaryCC-specific transmit power, denoted as P^(w2) _(CC)(i,j), where theavailable power is apportioned per the factor β(i,j), orP ^(w2) _(CC)(i,j)=P ^(w1) _(CC)(i,j)+β(i,j)·P ^(w)_(AWTRU)(i).  Equation (40)

For all CCs, the WTRU may then compute the signaled headroom as theratio of reduced second CC-specific transmit power to that of theoriginal requested CC-specific transmit power, in dB, or

$\begin{matrix}{P_{HCC}^{''} = {{10 \cdot \log}\; 10{( \frac{P_{CC}^{w\; 2}( {i,j} )}{P_{CC}^{w}( {i,j} )} ).}}} & {{Equation}\mspace{14mu}(41)}\end{matrix}$

To account for the maximum power of the PAs in addition to accountingfor the CC maximum power and the WTRU maximum power, the method mayinclude an option to combine first and last methods for signalingCC-specific power headrooms such that the WTRU signals the one headroomthat represents the least amount of headroom available in the WTRU,(i.e., the worst case scenario). This may correspond to choosing andsignaling as the headroom the lower value of P′_(HCC)(i,j) andP″_(HCC)(i,j).

Described herein is an example method for power headroom reporting (PHR)for fallback scenarios. In any given subframe, given N componentcarriers, the WTRU uses one of the up to 2^N combinations oftransmission schemes. When a PHR trigger occurs, power headroom may bereported by the WTRU for the one transmission scheme combination thatcoincidently is used at that subframe. For a given CC, power headroommay vary significantly between that experienced in the configured andfallback transmission schemes due to potentially different transmitpower requirements between the two transmission schemes. The basestation, relying only on power headroom reported for one particulartransmission scheme combination, may not have the complete set ofinformation available to make appropriate scheduling decisions for theWTRU.

In LTE R8, there one is periodic timer and one prohibit timer. Powerheadroom may be reported when either the periodic timer expires, orthere has been a large pathloss change since the previous headroomreport, and the prohibit timer has expired.

In the example method for multiple component carriers, the WTRU may haveone combination prohibit timer for each of the 2^N possible combinationsof transmission schemes, replacing, or in addition to, the WTRU(alternatively, CC-specific) prohibit timer for the WTRU (alternatively,for each CC). Each combination prohibit timer may be set/reset with adifferent value, or the same value. The set/reset value(s) may be fixed,or configured by the base station signaling a new parameter(s), similarto prohibitPHR-Timer.

When triggered, the WTRU may transmit power headroom concurrently forall component carriers for the current transmission scheme combination,and restart the prohibit timer for that combination, as well as theperiodic timer. Whenever the base station changes the WTRU'stransmission scheme combination, the WTRU may send the power headroomfor all active (alternatively all configured) component carriers for thenew transmission scheme combination, unless prohibited by thatcombination's prohibit timer (because of a recent power headroom reportfor that same transmission scheme combination).

For the case of all component carriers configured to be insingle-antenna port mode, fallback does not occur, and thus modificationof the trigger algorithm as shown results in power headroom beingreported as if the modification were not implemented.

An example implementation of the PHR for fallback is presented in Table3 as a modification to the power headroom reporting procedure, where theWTRU prohibit timers may be replaced by the combination prohibits timers

TABLE 3 Power Headroom Reporting The Power Headroom reporting procedureis used to provide the serving eNB with information about the differencebetween the nominal UE maximum transmit power and the estimated powerfor UL-SCH transmission. The reporting period, delay and mapping ofPower Headroom are defined in subclause 9.1.8 of [36.133]. RRC controlsPower Headroom reporting by configuring two types of timersperiodicPHR-Timer and prohibitPHR-Timer, and by signallingdl-PathlossChange which sets the change in measured downlink pathloss totrigger a PHR [36.331]. For N configured component carriers, there are2{circumflex over ( )}N separate timers, denoted asprohibitPHR-Timer(tsc), where tsc is an index, e.g., 0≦tsc<(2{circumflexover ( )}N), for each of the 2{circumflex over ( )}N transmission schemecombinations and current tsc is the index of the transmission schemecombination in the current subframe. There is a trigger, denoted astrigger(tsc), for each transmission scheme combination. A Power HeadroomReport (PHR) for all configured UL component carriers, active orinactive,(alternatively for all active UL component carriers) shall betriggered for the current transmission scheme combination if any of thefollowing events occur:   prohibitPHR-Timer(current tsc) expires or hasexpired and the path loss for any configured   (alternatively active)component carrier has changed more than dl-PathlossChange dB since   thetransmission of a PHR when UE has UL resources for new transmission;  prohibitPHR-Timer(current tsc) expires or has expired and the currenttransmission   scheme is different from the transmision scheme of theprevious transmission   periodicPHR-Timer expires;   upon configurationor reconfiguration of the power headroom reporting functionality by  upper layers [8], which is not used to disable the function. If the UEhas UL resources allocated for new transmission for this TTI:   if it isthe first UL resource allocated for a new transmission since the lastMAC reset,   start periodicPHR-Timer;   if the Power Headroom reportingprocedure determines that trigger(current tsc) is set or   this is thefirst time that a PHR is triggered, and;   if the allocated UL resourcescan accommodate a PHR MAC control element plus its   subheader as aresult of logical channel prioritization for all configured(alternatively all   active) UL component carriers:    obtain the valueof the power headrooms for all configured (alternatively all active)   component carriers from the physical layer;    instruct theMultiplexing and Assembly procedure to generate and transmit, for all   configured (alternatively all active) UL component carriers, a PHRMAC control element    based on the value reported by the physicallayer;    start or restart periodicPHR-Timer;    start or restartprohibitPHR-Timer(current tsc);    clear trigger for all tsc   else settrigger(current tsc) endif

A diagram illustrating the method of Table 3, which by way of exampleshows the use of three of the possible 2^N transmission schemecombinations, is shown in FIG. 5. As illustrated, an initial PHR forscheme 0 may be transmitted which is followed by another PHR uponexpiration of the scheme 0 periodic timer. A scheme 1 PHR is transmittedbased on changing to scheme 1. A second PHR is transmitted uponexpiration of the scheme 1 periodic timer. However, an event triggeredPHR for scheme 1 is prohibited as the scheme 1 timer is still active.Upon changing to scheme 2, an attempt to transmit PHR is prohibited dueto lack of medium access control (MAC) buffer space. A PHR triggered bythe change to scheme 2 is successfully transmitted at a later time.

Alternatively, the base station may signal separate prohibit timerstartup values for each transmission scheme combination, rather thansignaling just one prohibit timer startup value. Using one commonprohibit timer startup value or the signaling of separate such valuesmay be either fixed or configurable.

In another method, given that the transmission scheme combination haschanged since the previous transmission, and that the transmissionscheme combination's prohibit timer has not expired, rather than sendingpower headroom for all configured (alternatively all active) componentcarriers, the WTRU may send the power headroom for the componentcarrier(s) with changed transmission scheme(s). Alternatively, for atransmission scheme transition to all configured (alternatively allactive) component carriers using the configured transmission schemes, orall configured (alternatively all active) component carriers using thefallback transmission scheme, the WTRU may send power headroom for allconfigured (alternatively all active) component carriers. Otherwise, theWTRU may send power headroom reports just for the changed componentcarriers. The use of the methods may be fixed or configurable

The transmission scheme for a fake component carrier may be the fallbackscheme rather than the preferred configured scheme. The selection may beconfigurable, either common for all fake CCs or per component carrier.

Described herein are additional example methods for carrier aggregationtaking into account a WTRU maximum transmit power. When there is a WTRUmaximum transmit power, raising or lowering the transmit power of onecomponent carrier may impact the ability to raise the transit power inanother component carrier.

In one example method, the WTRU may compute and report power headroomfor a CC as if the base station scheduler would respond to only thatparticular reported power headroom, and not change the grants of theother CCs. For each component carrier, the WTRU may determine the powerheadroom as the smaller of the headroom with respect to the CC maximumtransmit power and the headroom with respect to the WTRU maximumtransmit power given that the transmit powers of all other componentcarriers remain unchanged. In this method, the WTRU reports one PH perCC.

An example of this method follows. Note that this is a simplifiedexample and as such all effects (such as maximum power reduction (MPR)and others) may not be taken into account. Also note that powerheadrooms are typically reported in decibel (dB) and watts are used herefor ease of illustration.

Given 2 CCs, CC1 and CC2, which, based on their grants, may transmit at0.75 W and 0.25 W, respectively. Also given are per CC maximum allowedtransmit powers of 1 W and a WTRU maximum allowed transmit power of 1 W.Taking only the per CC maximum into account, each CC appears to havepositive headroom. However, since the sum of the powers is 1 W, the WTRUhas no headroom with respect to the WTRU maximum. The WTRU may report no(0) headroom for both CCs indicating to the base station that it may notincrease the grant on one CC without decreasing the grant on the other.In another example, the WTRU limit may be given as 1.5 W. In thisexample, CC1 may be increased 0.25 W alone and CC2 may be increased 0.75W alone. The maximum the total may be raised is 0.5 W. CC1 would reportheadroom based on the CC limit (able to increase another 0.25 W) and CC2would report headroom based on the WTRU limit (able to increase another0.5 W). As a variation on this method, the WTRU may determine and reportboth the power headroom for each CC as described and the power headroomfor each CC with respect to its CC maximum power limit. Accordingly, theWTRU may report two power headrooms per CC.

Alternatively, the WTRU may determine and report power headroom inaccordance with both methods above. In this method, the WTRU may reporttwo power headrooms per CC. This method may use more PHR signaling thanthe method set forth above, but gives the base station the most completeset of information with respect to power headroom.

A variant of the above method and of the other methods described hereinfor which there is a WTRU maximum power limit may be to modify thenominal power headrooms of the multiple component carriers such that thebase station may act upon all reported power headrooms and not violateany maximum power constraint. For example, in each of these methods theWTRU may compute power headroom for each CC such that it may allocatemore headroom to higher priority CCs than lower priority. The WTRU mayfirst compute the actual (nominal) headroom for each CC and then adjustthe headrooms to report more positive headroom for higher prioritycomponent carriers over those of lower priority component carriers.Prioritization may be based on the type of CC, for example primary CC(PCC) may have priority over secondary CC(s) (SCC(s)). Prioritizationmay, alternatively, follow a rule similar to a maximum power procedureprioritization rule where, for example, PUCCH has highest priority,PUSCH with uplink control information (UCI) has next highest and PUSCHwithout UCI has lowest priority. In this case, the priority for headroomallocation may be based on which channel(s) the CC is carrying.

Power headroom may at times be reported for some combination of real andvirtual component carriers.

Component carriers transmitted simultaneously with other componentcarriers can result in intermodulation and other effects, which canimpact maximum transmission power, which in turn can impact percomponent carrier power headroom.

Methods for computing and reporting power headroom are described hereingiven that there may be real as well as virtual component carriers tosupport the base station in making scheduling decisions. In thesemethods, the effects due to the presence of the other CCs may includeeffects due to their transmit powers, intermodulation effects, impact onMPR, and/or the like. The example methods may use look up tables orcalculations that are based on the transmit characteristics of thechannels on the CCs (such as frequency, number of resource blocks andthe like).

When the WTRU reports a power headroom for a virtual CC, the WTRU maytransmit the power headroom on a real CC where the real CC may beconfigurable via signaling from the base station. Alternatively, theWTRU may autonomously determine a real CC for the virtual CC powerheadroom transmission. For example, the WTRU may use a real CC havingthe largest UL grant or the primary UL CC if it has a grant.

Described herein are example methods for power headroom reporting forreal CCs. In one example method, for a subframe which may contain bothreal UL CCs (component carriers with grants) and virtual UL componentcarriers (active, or configured, component carriers without grants), theWTRU may, for each real CC, compute the power headroom taking intoaccount the presence of (i.e., the effects due to the presence of) theother real CCs. The virtual CCs may be ignored when determining thepower headroom for the real CCs. The WTRU may report one power headroomfor each of the real CCs. This example method may represent the actualstate of the WTRU at the time of the headroom report. This method may beapplicable whether or not there are any virtual CCs in a given subframeand whether or not power headroom may be reported for virtual CCs in anysubframe.

In another method, for a subframe which may contain both real UL CCs(component carriers with grants) and virtual UL component carriers(active, or configured, component carriers without grants), the WTRUmay, for each real CC, compute the power headroom taking into accountthe presence (i.e., the effects due to the presence) of the other realCCs and the virtual CCs, assuming the virtual CCs are being transmittedwith the reference or otherwise specified formats. The WTRU may reportone power headroom for each of the real CCs. This method assumes thepresence of all CCs, both real and virtual, and as the presence ofadditional component carriers tends to raise MPR and lower maximumpower, this example method may provide the base station with aconservative estimate of additional power headroom.

Alternatively, the WTRU may compute the power headroom as described inthe above two methods, and report both. This method may use more PHRsignaling than does each of these methods but may give the base stationthe most complete set of information for power headroom.

In another alternative, it may be configurable via signaling from thebase station as to whether to report power headroom in accordance witheither of the two above disclosed methods. In this way, the base stationmay obtain the information it needs with only one PHR for each real CC.

Described herein are example methods for power headroom reporting forvirtual CCs. In an example method, for a subframe which may include bothreal UL component carriers (component carriers with grants) and virtualUL component carriers (active, or configured, component carriers withoutgrants), the WTRU may, for each virtual CC, compute the power headroomtaking into account the presence of (i.e., the effects due to thepresence of) all the real CCs. The other virtual CCs are ignored. TheWTRU may report one power headroom for each of the virtual CCs. Thismethod may be most useful for the case of the base station schedulingjust the one additional virtual component carrier (i.e., in addition tothe real CCs). As the presence of additional component carriers tends toraise MPR and thus lower maximum power, this example method may providethe base station with a liberal estimate of power headroom for thevirtual CCs.

In another method, for a subframe which may include both real UL CCs(component carriers with grants) and virtual UL CCs (active, orconfigured, component carriers without grants), the WTRU may, for eachvirtual CC, compute the power headroom as if none of the other CCs, realor virtual, were present, and report one power headroom for each of thevirtual CCs. This example method may be most useful for the case of thebase station scheduling only the virtual CC.

In another example method, for a subframe which may include both real ULCCs (component carriers with grants) and virtual UL CCs (active, orconfigured, component carriers without grants), the WTRU may, for eachvirtual CC, compute the power headroom taking into account the presenceof (i.e., the effects due to the presence of) all the real CCs and allthe other virtual CCs assuming the virtual CCs are being transmittedwith the reference or otherwise specified grant(s) or format(s), andreport one power headroom for each of the virtual CCs. This examplemethod may be most useful for the case of the base station schedulingall CCs. As the presence of additional component carriers tends to raiseMPR and lower maximum power, this example method may provide the basestation with a conservative estimate of power headroom for the virtualCCs.

In another method, the WTRU computes and reports each virtual CC powerheadroom as described in one or more of the methods for power headroomreporting for virtual CCs disclosed above. This method requiresadditional signaling.

Alternatively, it may be configurable via signaling from the basestation as to which method to use for computing and reporting PHR for avirtual CC. In this way, the base station may obtain the information itneeds with only one PHR for each virtual CC.

Described herein are example methods for including the power headroomreport(s) in one or more media access control (MAC) packet data unitsPDUs. In LTE R8, the power headroom control element may be identified bya MAC PDU subheader with logical channel ID (LCID) 11010. There are 15reserved logical channels i.e., logical channels 01011 to 11001 (inbinary notation) corresponding to LCIDs 11 to 27 in decimal notation.

In an example method, the reserved logical channels may be re-used insupport of CC specific or PA specific power headroom reporting. As partof a MAC configuration RRC message exchange between the base station andthe WTRU, a mapping between the CC and the PH reporting logical channelsmay be defined. The WTRU may construct PH reports based on the mappingbetween the CC and PH reporting logical channels provided by the basestation. Alternatively, the WTRU may autonomously define the mapping andcommunicate this mapping to the base station using an RRC message, forexample.

The LTE R8 power headroom MAC control element consists of 1 octet. Inthe example method, the 6 least significant bits may be used for theactual PH report and the 2 most significant bits may be reserved. In analternative method, the CC-specific and/or PA-specific PH may bereported by defining several 6-bit combinations from the 8 bit set.There are 28 combinations of 6 bits in 8 bits. A mapping between PH6-bit combinations and CC or PA may be exchanged between the basestation and the WTRU. The WTRU may then use for each CC, thecorresponding 6-bit combinations to report the power headrooms.

Described herein are example methods for controlling power headroomreporting. In LTE R8, the MAC power headroom reporting may be triggeredby three main events. In one case, the MAC power headroom reporting maybe triggered when the PROHIBIT_PHR_TIMER expires or has expired and thepath loss has changed more than DL_PathlossChange dB since the lastpower headroom report and the WTRU has UL resources for a newtransmission. In the second case, the MAC power headroom reporting maybe triggered when the PERIODIC_PHR_TIMER expires, in which case the PHRis referred to as “Periodic PHR”. In the third case, the MAC powerheadroom reporting may be triggered upon configuration andreconfiguration of a Periodic PHR.

In an example method for controlling power headroom reporting, thereporting methods described above may be applied on a CC basis and/or ona PA basis. The MAC configuration for PH reporting purposes (which mayinclude PERIODIC_PHR_TIMER, PROHIBIT_PHR_TIMER, DL_PathlossChangethreshold) may be provided to the WTRU by the base station on a CC basisand/or on PA basis. Upon the reception of these configurations, the WTRUmay apply them, i.e., use them for determining when to trigger PHreporting, on a CC basis and/or on PA basis.

In another method for controlling power headroom reporting, the WTRU maycontrol CC-specific and/or PA-specific PH reporting on a group basis,i.e., CCs and/or PAs may be grouped for the purpose of PH reportingcontrol. The WTRU may autonomously or in coordination with the basestation may decide the grouping. The set of CCs and/or PAs that arewithin the same group are PH reported using the same reportingconfiguration parameter set (which may include PERIODIC_PHR_TIMER,PROHIBIT_PHR_TIMER, DL_PathlossChange threshold) or a subset. The groupmay be the complete set of the CCs and/or PAs.

In another method for controlling power headroom reporting, the controlof the PH reporting may be done using a combination of the twoalternative methods above.

The methods may also include methods for disabling power headroomreporting on a CC basis, PA basis, or a combination of CCs and/or PAsbasis. Upon indication from a base station or autonomous determinationby the WTRU, the WTRU may disable PH reporting for the relevant CCsand/or PAs.

Described herein are example methods for RRC configuration of MAC forpower headroom reporting. The RRC protocol may be updated to configurethe MAC such that the CC and/or PA PH reporting algorithm(s) describedabove may be supported. In one method, the LTE R8 MAC configuration IE(MAC-MainConfiguration) may be replicated for each CC and/or each PA. Inanother method, the PH configuration IE (phr-Configuration) within theLTE R8 MAC configuration IE (MAC-MainConfiguration) may be replicatedper CC and/or per PA. In another method, RRC protocol updates mayinclude system information blocks (SIBs) update in support of CCspecific maximum power and/or PA specific maximum power as describedherein.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A method for reporting power headroom, the methodcomprising: calculating a physical uplink control channel (PUCCH)transmit power associated with a reference downlink control information(DCI) format in the absence of a PUCCH transmission; determining, via awireless transmit/receive unit (WTRU), a power headroom using a physicaluplink shared channel (PUSCH) transmit power and the PUCCH transmitpower; and sending the power headroom.
 2. A wireless transmit/receiveunit (WTRU), the WTRU comprising: a processor, the processor configuredto: calculate a physical uplink control channel (PUCCH) transmit powerassociated with a reference downlink control information (DCI) format inthe absence of a PUCCH transmission; determine a power headroom using aphysical uplink shared channel (PUSCH) transmit power and the PUCCHtransmit power; and send the power headroom.
 3. The method of claim 1,further comprising determining that the WTRU is configured forsimultaneous PUSCH/PUCCH transmission.
 4. The method of claim 1, whereinthe power headroom is a first power headroom, the PUSCH transmit poweris a first PUSCH transmit power, and the method further comprises:determining a second power headroom using a second PUSCH transmit power;and sending the first power headroom and the second power headroom inthe same subframe.
 5. The method of claim 4, wherein the first powerheadroom is for a carrier, the second power headroom is for the carrier,the first PUSCH transmit power is for the carrier, and the second PUSCHtransmit power is for the carrier.
 6. The method of claim 4, wherein thefirst power headroom is for a first carrier, the second power headroomis for a second carrier, the first PUSCH transmit power is for the firstcarrier, and the second PUSCH transmit power is for the second carrier.7. The method of claim 1, further comprising determining a carrier has aPUSCH transmission in a subframe.
 8. The method of claim 1, furthercomprising determining a maximum power for a carrier.
 9. The method ofclaim 8, wherein the maximum power for the carrier is a WTRU configuredmaximum output for the carrier.
 10. The method of claim 1, wherein thepower headroom is for a primary cell.
 11. The method of claim 1, whereinthe reference DCI format is a DCI format 1A.
 12. The method of claim 1,wherein determining the power headroom using the PUSCH transmit powerand the PUCCH transmit power comprises: determining a maximum transmitpower for a carrier; and calculating the power headroom using themaximum transmit power for the carrier, the PUSCH transmit power, andthe PUCCH transmit power.
 13. The WTRU of claim 2, wherein the WTRU isfurther configured to determine that the WTRU is configured forsimultaneous PUSCH/PUCCH transmission.
 14. The WTRU of claim 2, whereinthe power headroom is a first power headroom, the PUSCH transmit poweris a first PUSCH transmit power, and the processor is further configuredto: determine a second power headroom using a second PUSCH transmitpower; and send the first power headroom and the second power headroomin the same subframe.
 15. The WTRU of claim 14, wherein the first powerheadroom is for a carrier, the second power headroom is for the carrier,the first PUSCH transmit power is for the carrier, and the second PUSCHtransmit power for the carrier.
 16. The WTRU of claim 14, wherein thefirst power headroom is for a first carrier, the second power headroomis for a second carrier, the first PUSCH transmit power is for the firstcarrier, and the second PUSCH transmit power is for the second carrier.17. The WTRU of claim 2, wherein the processor is further configured todetermine that a carrier has a PUSCH transmission in a subframe.
 18. TheWTRU of claim 2, wherein the processor is further configured todetermine a maximum power for a carrier.
 19. The WTRU of claim 18,wherein the maximum power for the carrier is a WTRU configured maximumoutput power for the carrier.
 20. The WTRU of claim 2, wherein the powerheadroom is for a primary cell.
 21. The WTRU of claim 2, wherein thereference DCI format is a DCI format 1A.
 22. The WTRU of claim 2,wherein the processor is configured to determine the power headroomusing the PUSCH transmit power and the PUCCH transmit power comprises:determining a maximum transmit power for a carrier; and calculating thepower headroom using the maximum transmit power for the carrier, thePUSCH transmit power, and the PUCCH transmit power.